QuantumATK Forum

QuantumATK => General Questions and Answers => Topic started by: 7we on March 9, 2016, 19:09

Title: Molecular Energy Levels
Post by: 7we on March 9, 2016, 19:09

Could someone please help me to Identify the LUMO/HOMO energy levels for this molecular structures? and explain what does 1.70E+00 or 1.96E-01 occupancy mean?

| Fermi level = -4.130596e+00 |                   | Fermi level = -3.854812e+00 |            
| Number of electrons = 242.000343 |         | Number of electrons = 246.000138 |            
                           
                           
110   -2.23E+00   2.00E+00                  110   -2.73E+00   2.00E+00      
111   -2.19E+00   2.00E+00                  111   -2.68E+00   2.00E+00      
112   -2.15E+00   2.00E+00                  112   -2.66E+00   2.00E+00      
113   -2.13E+00   2.00E+00                  113   -2.65E+00   2.00E+00      
114   -1.95E+00   2.00E+00                  114   -2.53E+00   2.00E+00      
115   -1.18E+00   2.00E+00                  115   -2.50E+00   2.00E+00      
116   -1.13E+00   2.00E+00                  116   -2.44E+00   2.00E+00      
117   -1.00E+00   2.00E+00                  117   -1.69E+00   2.00E+00      
118   -9.85E-01   2.00E+00                  118   -1.68E+00   2.00E+00      
119   -9.02E-01   2.00E+00                  119   -1.59E+00   2.00E+00      
120   -5.84E-04   1.01E+00                  120   -1.44E+00   2.00E+00      
121   5.66E-04   9.89E-01                  121   -1.41E+00   2.00E+00      
122   6.62E-01   1.49E-11                    122   -4.48E-02   1.70E+00      
123   7.29E-01   1.15E-12                     123    5.74E-02   1.96E-01      
124   8.83E-01   2.88E-15                  124   7.49E-02   1.05E-01      
125   1.22E+00   6.85E-21                  125   2.97E-01   2.08E-05      
126   1.72E+00   2.58E-29                  126   6.73E-01   1.00E-11      
127   1.86E+00   1.03E-31                  127   9.17E-01   7.91E-16      
128   1.98E+00   9.77E-34                  128   9.42E-01   3.04E-16      
129   2.49E+00   2.50E-42                  129   1.46E+00   7.18E-25      
130   2.60E+00   7.44E-44                  130   1.70E+00   5.53E-29      

Thanks

Title: Re: Molecular Energy Levels
Post by: Jess Wellendorff on March 10, 2016, 08:58

What sort of analysis does this output come from? Does not look like a MolecularEnergySpectrum for a molecular configuration....

Occupancy = 2.0 means 2 electrons in that state, a spin-up and a spin-down electron (full occupancy). Without spin-polarization, anything less than 2 means partial or no occupancy.

But I do not understand how you can have partial occupancy in a molecular system. Would expect either 2 or 0, like in the MolecularEnergySpectrum below.

Code

+------------------------------------------------------------------------------+
| Molecular Energy Spectrum Report                                             |
---------------------------------------------------------------------------- |
| Fermi level = -4.550063e+00                                                  |
| Number of electrons = 52.000000                                              |
| Unit = eV                                                                    |
| Eigenenergies given relative to the Fermi Level                              |
+------------------------------------------------------------------------------+
   22  -4.396009e+00   2.000000e+00
   23  -4.265472e+00   2.000000e+00
   24  -2.548539e+00   2.000000e+00
   25  -2.350585e+00   2.000000e+00
   26   2.350626e+00   6.490006e-40
   27   2.521805e+00   8.641132e-43
   28   6.023727e+00   7.440152e-44
   29   6.490207e+00   7.440152e-44
   30   7.177419e+00   7.440152e-44
   31   7.301969e+00   7.440152e-44

Title: Re: Molecular Energy Levels
Post by: 7we on March 10, 2016, 22:45

These are the Molecular Energy Spectrum of a C60 molecule, after one of the carbon atom is replace by tungsten. So it is a C59W (optimized structure). Is it possible to indicate to LUMO and HOMO of a structure like this from the provided energy levels?
Thanks again for the reply.

Quote from: Jess Wellendorff on March 10, 2016, 08:58

What sort of analysis does this output come from? Does not look like a MolecularEnergySpectrum for a molecular configuration....

Occupancy = 2.0 means 2 electrons in that state, a spin-up and a spin-down electron (full occupancy). Without spin-polarization, anything less than 2 means partial or no occupancy.

But I do not understand how you can have partial occupancy in a molecular system. Would expect either 2 or 0, like in the MolecularEnergySpectrum below.

Code

+------------------------------------------------------------------------------+
| Molecular Energy Spectrum Report                                             |
---------------------------------------------------------------------------- |
| Fermi level = -4.550063e+00                                                  |
| Number of electrons = 52.000000                                              |
| Unit = eV                                                                    |
| Eigenenergies given relative to the Fermi Level                              |
+------------------------------------------------------------------------------+
   22  -4.396009e+00   2.000000e+00
   23  -4.265472e+00   2.000000e+00
   24  -2.548539e+00   2.000000e+00
   25  -2.350585e+00   2.000000e+00
   26   2.350626e+00   6.490006e-40
   27   2.521805e+00   8.641132e-43
   28   6.023727e+00   7.440152e-44
   29   6.490207e+00   7.440152e-44
   30   7.177419e+00   7.440152e-44
   31   7.301969e+00   7.440152e-44

Title: Re: Molecular Energy Levels
Post by: Jess Wellendorff on March 11, 2016, 08:36

In the MolecularEnergySpectrum report that I posted, the HOMO is state #25 (fully occupied) and the LUMO state #26 (not occupied at all). The HOMO-LUMO gap is quite large, 4.7 eV:

Code

   25  -2.350585e+00   2.000000e+00
   26   2.350626e+00   6.490006e-40

However, in your calculation, it is not clear which is which, because you have partly occupied states:

Code

119   -9.02E-01   2.00E+00    119   -1.59E+00   2.00E+00      
120   -5.84E-04   1.01E+00    120   -1.44E+00   2.00E+00  
121    5.66E-04   9.89E-01    121   -1.41E+00   2.00E+00      
122    6.62E-01   1.49E-11    122   -4.48E-02   1.70E+00      
123    7.29E-01   1.15E-12    123    5.74E-02   1.96E-01    

You see that the HOMO-LUMO gaps are very small, on the order of a 1 meV, which is why the Fermi smearing of electronic occupations around the Fermi level leads to non-integer occupations. I suggest you try to decrease the electron temperature in order to get integer occupations, which should be expected for an isolated molecule.

Title: Re: Molecular Energy Levels
Post by: Anders Blom on March 11, 2016, 13:01

As always, if you want help for a specific system, post the input script.

Title: Re: Molecular Energy Levels
Post by: 7we on March 13, 2016, 19:18

Thanks again for the reply.
These are some parameters that I used to calculate the Molecular energy levels of C59W and I attached the script too.
Exchange Correlation: None  ////////       Mesh Cutoff :75.0 Hartree
Poisson Solver: MG         ////////                 SCF Iterations: Yes
Basis Sets:   Carbon: FHI [Z=4] DoubleZetaPolarized        ////  Tungsten: FHI [Z=6] DoubleZetaPolarized
 exchange=DiracBloch,
 correlation=VoskoWilkNussair,
I tried to use lower electron temperature as you suggested, but now I have a new problem. first thing I noticed if I repeat a simulation without changing any of the parameters, the total #of electrons changes (e.g #e: 242.248413,  241.984365, 240.172426) while everything else including TEnergy, or Fermi stay constant. I would appreciate if you can explain this difference between the # of electron that appears in my calculation even though I am running the same script.

Thanks again for your time.